1. Field of the Invention
The present invention relates to a stepping motor control unit and an analogue electronic watch using the stepping motor control circuit.
2. Description of the Related Art
In the related art, a stepping motor including a stator having a rotor storage hole and a positioning portion for determining a stop position of a rotor, the rotor disposed in the rotor storage hole, and a coil, and being configured to rotate the rotor by causing the stator to generate a magnetic flux by supplying alternating signals to the coil and stop the same at a position corresponding to the positioning portion is used in an analogue electronic watch, for example.
A method employed as a method of controlling the stepping motor is a correction drive system configured to detect whether or not the stepping motor is rotated by detecting an induced signal VRs generated in the stepping motor when the stepping motor is driven with a main drive pulse P1 and, according to the result of detection of whether or not the stepping motor is rotated, change the pulse width of the main drive pulse P1 and drive the stepping motor with the changed main drive pulse P1 or forcedly rotate the stepping motor with a correction drive pulse P2 having a pulse width larger than that of the main drive pulse P1 (for example, JP-B-61-15385).
WO2005/119377 discloses a unit for comparatively discriminating the detected time and the reference time in addition to the detection of the induced signal when detecting the rotation of the stepping motor. If the detected signal is lower than a predetermined reference threshold voltage Vcomp after having rotated the stepping motor with a main drive pulse P11, the corrected drive pulse P2 is supplied, and the subsequent main drive pulse P1 is changed to a main drive pulse P12 having a larger energy than the main drive pulse P11 for driving the stepping motor (upgrade). If the detected time of the rotation with the main drive pulse P12 is earlier than the reference time, the main drive pulse P12 is changed to the main drive pulse P11 (downgrade). In this manner, the pulse is controlled to rotate the stepping motor with the main drive pulse P1 according to the load by determining the state of rotation of the stepping motor when being driven with the main drive pulse, so that the current consumption is reduced.
However, if an attempt is made to determine the state of rotation of the stepping motor only on the basis of whether or not the time of day when the induced signal VRs is generated is earlier than the reference time, determination of the amount of the excess or the shortage of the energy of the main drive pulse with respect to the load is difficult. Therefore, further adequate pulse control is not achieved, and hence an unstable rotation and a limited reduction of power consumption are resulted.